Since the discovery that there would be theoretically very high magnetic properties [(BH) max.about.50 MGOe] when rare earth metals and transition metals are combined into metal compounds in a ratio of 2:17 to form a rare earth-transition metal alloy, there have been a number of attempts to obtain practical permanent magnet applications using these types of compounds. One example is the Sm-Co-Cu-Fe metal compound where (BH)max has reached .about.30 MGOe. Further, with Nd-Fe metal compounds, high magnetic properties of (BH)max.about.40 MGOe have been reached. These alloy formulations are crushed into powder, and then aligned and compression formed in a magnetic field, or formed in a non-magnetic field, sintered, solution-treated, and aged to form a mass, and then cut and polished into permanent magnets of the shape required according to the most usual methods of their preparation. Since the rare earth and ferrous type permanent magnets, particularly the R-Fe-M permanent magnets (where R represents one or more types of rare earth metals, and M represents B or other metalloid element), are easily oxidized when exposed to air, when they are used in precision applications, such as in miniature electronic parts for magnetic circuits using permanent magnets, there are many instances were oxidation caused by exposure of the magnet to air leads to a degradation of the magnetic properties and fluctuations in their permanence due to changes in the magnetic space. Because of this, the prior art has used Cr or Ni plating to cover the surface to prevent this oxidation.
When wet type plating means are used, however, the surface of the permanent magnet itself can be corroded by the degreasing and oxidation removal processes, which makes plating difficult. In addition, following the plating operation, gaps sometimes exist between the permanent magnet surface and the plating. Peeling of the plating is likely in these areas. Also, pinhole defects are common. Overall magnetic properties are additionally likely to be affected by the numerous processing steps involved, sintering, solution treating, aging, machining (cutting grinding and polishing) to obtain the desired magnetic properties and shape, etc., which are apt to lead to surface defects. FIG. 1A shows a graph of the resulting demagnetization curve where the effects above types of defects can be seen. These phenomena are especially dramatic in permanent magnets which have a relatively small volume but a relatively large surface area. Such defects result in lower producton yields.